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DOI: 10.1055/s-0043-1775504
Sterically Controlled Template-Assisted Macrocyclization of Hemisquaraine Rotaxanes: Synthesis, Characterization, and DFT Calculations
Authors
This work was supported by the National Research Foundation of Ukraine, project No. 2023.05/0003 titled ‘Development of new materials based on supramolecular systems for biomedical and veterinary applications’.
Abstract
The encapsulation of squaraine dyes within a tetralactam macrocycle effectively mitigates their intrinsic limitations while maintaining favorable optical properties and improving both chemical and photochemical stability. However, the synthesis of such rotaxanes remains challenging due to the intricate balance of steric and electronic factors governing the macrocyclization. In this study, a series of rotaxanes derived from hemisquaraine dyes bearing primary and secondary amino groups was successfully synthesized using an oxocyclobutenolate template-assisted macrocyclization approach. Dyes with bulky tertiary amino groups, however, failed to undergo encapsulation. Upon encapsulation, the rotaxane systems in chloroform exhibited red-shifted absorption and emission bands, along with a substantial increase in fluorescence quantum yield. This enhancement is attributed to the restricted vibrational and rotational motions of the encapsulated dye. DFT calculations confirmed that all studied rotaxanes are thermodynamically viable, suggesting that the synthetic difficulties observed for tertiary amine derivatives arise from kinetic constraints. This hypothesis was supported by DFT calculations that simulated the macrocyclization process from the corresponding open-chain precursors. These calculations showed favorable energetics for hemisquaraine dyes that contain primary and secondary amino groups. In contrast, the significant steric effects of tertiary amino groups render the oxocyclobutenolate template-assisted macrocyclization energetically unfavorable.
Key words
template-assisted macrocyclization - squaraine dye - DFT calculations - fluorescence - rotaxane - organic synthesis - optical absorption - supramolecular systemSupporting Information
- Supporting information for this article is available online at https://doi.org/10.1055/s-0043-1775504.
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Publication History
Received: 29 October 2025
Accepted after revision: 03 December 2025
Article published online:
05 January 2026
© 2026. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by/4.0/)
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